A portable trimmer, such as a shoulder-type portable trimmer, a backpack-type portable trimmer, a hedge trimmer or the like, generally employs a driving mechanism which transmits the power generated by an internal combustion engine to a cutter through a centrifugal clutch. In these portable trimmers, a brake device typically includes a friction member, such as a brake shoe or a brake band, which slidably engages with a clutch drum of the centrifugal clutch to prevent a cutter from free rotation. In operation, when an operator grips a brake lever, the brake device is actuated to stop rotation of the clutch drum and the cutter is prevented from being rotated unexpectedly. After having released the brake lever and thereby de-activating the brake device, the operator holds a throttle lever, adjusts a throttle opening of a throttle valve to control the power from the internal combustion engine, and thereby drives the cutter through the clutch drum to perform trimming work.
In this type of trimmer, however, if the brake device is released while the throttle lever is being gripped, the cutter might suddenly start to rotate at high speed before the safety at surrounding work operations is confirmed and might possibly cause a serious accident.